The present invention relates to remote control systems and, in particular, to systems in which the remotely controlled device is expendable.
Primarily, the present system is intended for use as a light weight, expendable balloon flight termination command receiver, although other potential uses are contemplated particularly in situations requiring high sensitivity, temperature tolerance, low power, low cost, low false triggering in high noise environments and, as an added bonus or adjunct to these characteristics, the capability of obtaining accurate range information for the device being controlled.
For some time a need has existed for a command receiver that can be used on balloon flights where recovery is not practical even though highly sensitive and reliable balloon control is required. Balloon flights present some special and quite difficult problems including, in addition to the need for expendability, the fact that the balloons frequently are operated at extreme altitudes and, at times, in a very high noise environment. Consequently, the command receiver must be highly sensitive and it also should provide a high degree of noise immunity to avoid accidental release. Also, because the receiver components are exposed to extremely low temperatures, they are highly susceptible to temperature drift which can prevent command reception or degrade the sensitivity and reliability.
In the past units used for these purposes mostly employed single or multiple constant tones decoded with tuned or RC circuits or, at times, with tone reed relays. These circuits all suffer from low sensitivity to false triggering comparisons and also are susceptible to drift with temperature. They do have one advantage in that a number of different commands can be sent on a single radio channel. However, as will become apparent, the present command receiver easily can be provided with additional circuitry which should make available as many, if not more, such channels.
Other serious disadvantages of the prior art techniques include such factors as their relatively high cost, power consumption and, significantly, the need for tuning during assembly. It also is quite desirable to provide a system with the capability of ranging or distance measuring and, in contrast to some of the prior art techniques, the present system readily adapts to this function and it therefore is provided as an added bonus to the command reception capability.